1. Field of the Invention
The present invention relates to a semiconductor laser module.
2. Description of the Related Art
For example, as a wavelength-tunable light source for use in dense wavelength division multiplexing (DWDM) optical communication, an integrated-type semiconductor laser element in which a plurality of semiconductor lasers having different laser oscillation wavelengths from each other are integrated is disclosed (for example, see Japanese Laid-open Patent Publication No. 2005-317695). This kind of integrated-type semiconductor laser element serves as a wavelength-tunable laser by switching a semiconductor laser for operation and changing a wavelength of laser light to be outputted. An optical coupler and a semiconductor optical amplifier (SOA) are connected to the plurality of semiconductor lasers in this order. The laser light emitted from the operated semiconductor laser and passing through the optical coupler is subject to optical amplification and outputted from an output end of the element. The integrated-type semiconductor laser element is mounted on a temperature-adjusting element for temperature adjustment of the element and enclosed in a casing to configure a semiconductor laser module. Such a semiconductor laser module is combined with an external modulator to be used as a signal light source for a long-haul optical transmission, for example, in a DWDM optical communication network system. Japan Patent No. 4639578 discloses a semiconductor laser module configured to optically amplify a laser light outputted from a distributed feedback (DFB) laser element with an SOA.